Here are a dozen succinct facts about the domestic cat purr. The text is deliberately ‘tight’ so that you can get through it fast. There are more articles on the cat purr at the base of the page for more extensive reading.
- Domestic cats purr under a number of circumstances: when content, when injured, when frightened, when suckling, when giving birth and even when close to death.
- The big cats: lions, tigers, leopards and jaguars can’t purr because their vocal mechanisms are designed for roaring. Their anatomy isn’t stiff enough to produce a purr.
- There have been a number of theories as to how cats make the purring sound including the “false vocal cord theory and the “turbulent blood theory”. The best answer is spelled-out by Sarah Hartwell (messybeast.com). She says that it is a “non-vocal sound caused by vibration of structures in the throat”. Studies have detected laryngeal muscles which have regular patterns associated with purring. These muscles contract when the mouth is closed and the glottis closed partially which results in a buildup of pressure behind or inside the glottis, which is the space between the vocal cords. This results in turbulent air as it passes through the narrow opening as the purr is produced. It happens on inhalation and exhalation.
- A kitten purrs when drinking milk from her mother. Often, they knead at the same time (to encourage milk flow) which is why you see adult cats kneading, for example, bed clothes or item of clothing of their caregiver while purring at the same time. They are reenacting what they did when they were newborn kittens suckling at their mother’s breast. Adult cats are kept in an extended period of kittenhood because they are provided for by their human caretaker.
- Dr. Desmond Morris thinks that there is a single overarching reason why cats purr and which fits all cases. He states that “purring signals a friendly social mood”. He goes on to state that it can be given as a signal indicating the need for friendship or as a signal to a caregiver as thanks for their friendship given. Others have suggested that the purr is a signal that the animal is not posing a threat. In Dr Morris’s later book Catlore he states that the purr signals, “I am inoffensive.” He also says that, “It is essentially a signal that says the cat is in a non-hostile mood, is friendly, submissive, reassuring, appeasing or, of course, contented.”
- A mother purrs to her kittens as they feed. She is telling them that she is relaxed while her kittens purr to tell her that all is well. They maintain contact with each other.
- Sarah Hartwell says that there is a “purr centre”. This is the ‘operation room’ in the cat’s brain which controls purring. The movement of the laryngeal muscles are signaled by unique ‘neural oscillator’ in the cat’s brain. The purr centre is connected to the hypothalamus, an area of the brain which interprets emotions and which decides both pleasant and painful sensory stimuli. She says that if a stimulus is pleasant the hypothalamus releases endorphins which stimulates the purr centre resulting in the production of the purr. Pain also stimulates the hypothalamus to release endorphins to block the pain which is also why cats purr when they are in pain.
- The fact that cats purr when injured suggest that the sound has a healing property much in the way that ultrasound can be used alongside physiotherapy to heal people. Low-frequency vibrations can aid bone growth and help repair bones, tendons and muscles. Domestic cat bones tend to heal rapidly and this may in part be due to the healing properties of their purr.
- Cats can sometimes purr when they are stressed and anxious. Timid cat might purr when settling into a new environment. It sounds faster than the more relaxed variant. The ‘stress purr’ gives way to the more relaxed version as the cat becomes more familiar with her surroundings. It is suggested that the stress purr is analogous to the nervous smile in humans.
- Cats can sometimes purr when requesting something. Normally cat request something from their caregiver with a meow. But there is a version of the purr which is described as a ‘soliciting purr’ which incorporates a vocalisation which has the frequency of the sound produced by a human baby. This sound may have evolved over 10,000 years of domestication in order to attract the attention of human caregivers.
- A reason why cats purr when they are in pain is because it helps to soothe them. This is described as the “self-soothing purr”.
- The classic instance when cats purr, as we all know, it when they are content such as when being petted or sitting on your lap. This is the “happy purr”.
My thanks to Sarah Hartwell (messybeast.com) and Dr Desmond Morris (CATWATCHING and Cat World).
SOME MORE ON THE CAT PURR:
Purring is caused by a simple airflow over connective tissue masses embedded in the vocal fold of the larynx
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